Touch and Proprioception

Question 1

Be able to recognize the relationship between conduction velocity, afferent axon diameter, and stimulus threshold of sensory fibers

Answer 1

• Larger axon diameter=faster conduction velocity. A-alpha fibers are largest, lowest threshold (most sensitive)

Question 2

• Be able to describe the importance of Na+ channels to sensory perception

Answer 2

• Mechanoreceptors work via sodium channels

Question 3

• Be able to recognize 3 different types of ion channels in mechanoreceptors

Answer 3

• Lipid tension: cell membrane stretched, structural proteins: linked to ion channels, indirect action: membrane structural proteins cause channels to open

Question 4

• Be able to define receptor types for proprioception, mechanoreception, thermoreception, and nociception

Answer 4

Proprioception: Muscle Spindles and Type 2 SA
Mechanoreception: Type 1 SA, Type 1 RA, Type 2 SA, Type 2 RA
Thermoreception: Warm and Cold
Nociception (pain): Mechanical, thermal and polymodal

Question 5

• Be able to recognize the fiber size nomenclature for each fiber size and be able to recall their approximate conduction velocity and the general sensory stimuli they respond to

Answer 5

• A alpha=fastest, proprioception. A beta=next fastest, find touch, stretching, pressure, proprioception. C= slowest, warmth and burning pain. A delta, C=faster than C, cold and sharp pain.

Question 6

• Be able to describe the difference between type 1 and type 2 sensory receptors in the skin.

Answer 6

• Type 1: surface receptors, small receptive field. Type 2: deep receptors, large receptive field.

Question 7

• Be able to describe the stimulus-response properties of rapidly and slowly adapting (RA and SA) skin receptors.

Answer 7

• Rapidly adapting=fire in response to change in status of stimulus (onset and offset). Slowly adapting=consistent firing.

Question 8

• Be able to classify Merkel’s disks, Meissner corpuscles, Pacinian corpuscle and Ruffini corpuscles into RA and SA types.

Answer 8

• Mechanoreception: Merkel=SA, type 1, Meissner=RA, type 1 (skin motion), Pacinian=RA, type 2 (vibration), Ruffini=SA, type 2 (stretch)

Question 9

• Be able to define and compare the receptive fields of different mechanoreceptors

Answer 9

• Type 2 larger fields than type 1

Question 10

• Be able to identify different types of nociceptors and describe their function

Answer 10

• Thermal: Ad, painful temperature, TRPs
• Mechanical: Ad, puncture, squeeze or pinch
• Polymodal: C, high intensity
• Silent: visceral

Question 11

• Be able to define TRP receptors

Answer 11

• Transient receptor potential: respond to different stimuli, temperature-like stimuli

Question 12

• Be able to identify the function and organization of the muscle spindle and the Golgi tendon organ

Answer 12

• Proprioception. Muscle spindle=group 1a fibers which detect change in length and group 2 fibers that detect length (statically). Golgi tendon organ: group 1b fibers which detect tension of muscle and contact inhibitory interneurons.

Question 13

• Be able to compare and contrast the function of the muscle spindle vs. the Golgi tendon organ

Answer 13

• Muscle spindle: length and change in length. Golgi: tension of muscle, prevents overcontraction, fine tension control.

Question 14

Organize receptor types into small and large receptive fields

Answer 14

Small: Merkel, meissner; Large: pacinian, ruffini

Question 15

Active touch vs. passive touch

Answer 15

Active: movement on an object, requires more cortical involvement. passive: object resting in hand

Question 16

Be able to identify different types of nociceptors and describe their function

Answer 16

Respond to different stimuli depending on TRP, multimodal. thermal and mechanical=a delta fibers, polymodal=C fibers, silent=mainly visceral (inflammation only)